Year	constant 2011 PPP $ per kg of oil equivalent
1990	4.25078765964533
1991	4.5788767669497
1992	4.88336427365168
1993	5.25802927577566
1994	4.5818918565566
1995	4.83856005278261
1996	5.00299661759057
1997	5.41469484293447
1998	5.58507416570631
1999	5.18642072683952
2000	5.83478029971269
2001	5.93208991560492
2002	5.81550616581007
2003	6.44509724871135
2004	6.69783544459905
2005	7.06728492912095
2006	7.24169743095667
2007	8.35128467587174
2008	8.8603060761364
2009	8.84312069860727
2010	8.95518861721397
2011	8.80627878923301
2012	10.2968044485195
2013	10.5225124349351
2014	10.5460630716295